1. Field of the Invention
The present invention relates to a dielectric paste useful as a load capacitor-forming material in a ceramic oscillator. The invention also relates to a thick-film capacitor using such a dielectric paste.
2. Description of the Related Art
Thick-film capacitors have been used as elements of thick-film integrated circuits and in other applications. Such thick-film capacitors generally include a barium titanate-based ceramic as a main component and a glass component or the like as an optional component. For example, Japanese Laid-Open Patent Publication No. 51-48159 discloses a dielectric substance consisting of a BaTiO.sub.3 --CaSnO.sub.3 --CaSiO.sub.3 -based ceramic. Japanese Laid-Open Patent Publication No. 51- 150097 discloses dielectric substances made from BaTiO.sub.3 --(Pb, Sr) (Ti, Sn)O.sub.3 and glass.
Such thick-film capacitors have been prepared in the manner described below. Specifically, a dielectric paste is prepared by dispersing a powder of the above-described dielectric substance in an organic vehicle. In some cases, powdered glass may be added to the vehicle. Then the paste is applied to an insulating substrate made of alumina, for example, by screen printing or other method. A plurality of such substrates are combined to form a laminate which is subsequently baked in air, thus completing the thick-film capacitors.
As digital IC technology evolves, ceramic oscillators using piezoelectric ceramics have been frequently employed as devices for generating reference signals in electronic instruments. Normally, a capacitor which is necessary for construction of an oscillator circuit is connected to such a ceramic oscillator. Since electronic devices have decreased in size in recent years, there is an increasing demand for miniaturization of electronic parts such as ceramic oscillators.
Accordingly, attempts have been made to fabricate ceramic oscillators incorporating thick-film capacitors instead of discrete type capacitors as load capacitors used for connection with the ceramic oscillators. However, the conventional dielectric paste contains a large percent of dielectric powder in order to obtain a high dielectric constant. Thus, there arises a problem in that the dielectric film obtained using the dielectric paste is not dense because the powder has a low density. In order to compensate for the low density, a plurality of layers of the dielectric paste must be used in order to increase film thickness. Moreover, in order to make the film more compact, it has been necessary to bake the dielectric film at a high temperature exceeding 900.degree. C.